1. Field of the Invention
The present invention relates to thin-film magnetic heads for applying a magnetic filed to a magnetic recording medium for writing, and particularly to a thin-film magnetic head including a magnetic pole which is easily prepared in such an appropriate shape as to prevent the occurrence of side fringing, and having enhanced characteristics. The present invention also relates to a magnetic device including the thin-film magnetic head and a method for manufacturing the magnetic head.
2. Description of the Related Art
FIG. 15 is a fragmentary enlarged front view of an upper magnetic pole layer, a gap layer, and lower magnetic pole layer shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2002-197616.
The side surfaces of the upper magnetic pole layer and lower magnetic pole layer slant so that the widths in the track width direction of the magnetic pole layers increase in the directions away from the gap layer, as shown in FIG. 15.
In FIG. 15, the widths in the track width direction of the bottom surface of the upper magnetic pole layer and the top surface of the lower magnetic pole layer are both defined as Tw5.
The shape of the magnetic pole shown in FIG. 15, however, has problems below. FIG. 16 is a schematic illustration for pointing out a problem when the thin-film magnetic head of the above-mentioned patent document moves over a recording medium in practice.
The diagonally shaded area in FIG. 16 shows a region (track) of a recording medium where recording has been made or will be made from the magnetic pole. As shown in FIG. 16, the magnetic pole moves over the recording medium in a slanting position with a predetermined angle θ5. This predetermined angle θ5 is referred to as skew angle.
When the bottom surface of the upper magnetic pole layer and the top surface of the lower magnetic pole layer have the same width of Tw5, as shown in FIG. 15, the skew angle θ5, as shown in FIG. 16, allows an edge of the top surface of the lower magnetic pole to run off the recording region. Consequently, the edge erases the recording magnetic field in the adjacent region where recording has already been made, or rewrites, and thus side fringing occurs seriously.
In Japanese Unexamined Patent Application Publication No. 2002-92818 and U.S. Pat. No. 6,055,138, the width Tw6 in the track width direction of the top surface of the lower core layer is smaller than the width Tw7 in the track width direction of the bottom surface of the upper core layer, as shown in FIG. 17. This structure of the thin-film magnetic head is expected to prevent the occurrence of side fringing.
It is not, however, clear whether this structure actually prevent side fringing effectively.
Specifically, the side fringing cannot be prevented by only controlling the structure of the thin-film magnetic head, and the relationship with the skew angle is an important factor. However, the two patent documents describe only the structure of the thin-film magnetic head, but not the relationship with the skew angle. For example, while the above-mentioned Japanese Unexamined Patent Application Publication No. 2002-92818 states a problem of the known art at a skew angle of 0°, with reference to FIG. 12 of the document, it does not state whether the structure shown in FIG. 11 of the same document having a skew angle prevents the side fringing effectively.
In the above-mentioned two patent documents, the lower core layer and the upper core layer oppose each other with a gap layer therebetween, at the opposing face to the recording medium. Thus, the structure is not such that magnetic pole layers separate from the core layers oppose each other with a gap layer therebetween.
Accordingly, the lower core layer and the upper core layer extend long in the height direction from the recording medium-opposing face, and are magnetically coupled at the back in the height direction to define a magnetic circuit.
Since the lower core layer and the upper core layer do not require only to be provided in the vicinity of the medium-opposing face, it is very difficult to reduce the track width with high precision so as to realize high recording density. Thus, this structure is liable to degrade recording properties.
In addition, since the lower core layer extends long in the height direction from the medium-opposing face, a coil layer has no choice but to be provided above the lower core layer. Thus, it is limited where the coil layer is provided. It is important that the region where the coil layer is formed can be selected from a wide range of areas, from the viewpoint of achieving a miniaturized thin-film magnetic head.
Furthermore, the above-mentioned two patent documents do not specifically describe how the structure is formed in which the top surface of the lower core layer has a smaller width Tw6 than the width Tw7 of the bottom surface of the upper core layer. Although the Japanese Unexamined Patent Application Publication No. 2002-92818 proposes a manufacturing method shown in FIGS. 5 to 10, these figures illustrate a method for manufacturing a thin-film magnetic head in which the width Tw6 of the top surface of the lower core layer and the width Tw7 of the bottom surface of the upper core layer are the same.